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Boron deficiency limits soy yields

Boron deficiencies in some Arkansas soybean fields were identified two years ago. But the problem seems to have been around a lot longer than that.

“A farmer in Green County told me he'd seen this problem before. He thought it was nematodes or even a virus. But after looking at the boron deficiency symptoms, he realized that he had the same troubles in his fields,” says Leo Espinoza, Arkansas Extension soil specialist. “We don't know if this is problem is increasing, how long it's been around, or if it just appeared a few years ago.”

Espinoza spoke at the annual Arkansas Soybean Research Conference in Brinkley, Ark.

“Another farmer said he has seen this problem in his fields since the 1970s. He farms a short distance north of Brinkley and his neighbor also has the problem.” Anecdotally, most of the affected locations have been north of I-40 and west of Crowley's Ridge.

Typical symptoms include greener and thicker leaves with a tendency to “cup” downwards. The nodes often are short and the terminal sometimes will die. Some plants recover through growth of lateral branching, but by then yield potential has been impaired. Yield losses in such cases can be more than 50 percent of expected yields.

“As we walked through fields, we saw healthy plants immediately beside very sick ones. It's strange because we see this problem across an entire field sometimes. Other times, we see it in patches or long strips within a field that's seemingly healthy otherwise.

“Are we dealing with a problem related to the chemistry of boron or is the problem one of soil management? When it comes to boron, most research has been done on toxicity levels and not deficiencies.” What's curious is that cereal crops — rice and wheat — have a higher requirement for boron than soybeans. Those crops' sufficiency levels are supposedly lower than those of soybeans. With all the rice and wheat Arkansans grow, however, “we don't have reports of boron deficiency. That doesn't mean it isn't there, but it certainly isn't showing up in a way that's obvious.”

To illustrate the problems researchers have in studying boron, Espinoza points to a large, infrared, birds-eye-view photo. (Espinoza is working on the boron project with both Nathan Slaton, Arkansas Extension director of soil testing, and Morteza Mozaffari, Cotton Branch soil lab director.)

“This is a soybean field that had a severe deficiency several years ago. We set up a large test there. Fortunately for the grower — but unfortunately for the test — the field's deficiency cleared up. This seems to happen regularly. We want to know why the deficiency was evident two years ago and not now.”

It's easy to see deficiencies through other infrared shots. One photo shows a field that typically yields soybeans in the low 50 bushels. Once deficiencies hit, however, it cut in the upper 20s.

“We're talking about large amounts of money lost. This isn't just taking a few pennies away,” says Espinoza.

In preparing a study, Espinoza and his colleagues were introduced to a boron-deficient field. The team took tissue samples around the V-6 stage and also at the R-2 stage.

A tissue sample of less than 20 parts per million raises a red flag of deficiency. When the levels are higher than 60 parts per million, boron may be at a toxic level. The field in question had plants testing 14 parts per million.

So, the researchers put foliar material out at 1 to 6 pounds per acre in six plots. Through later tissue samples they found that 4 to 6 pounds of material may have raised levels into the toxicity range. Plots receiving between 1 pound and 4 pounds raised the boron tissue levels to the sufficiency range. The 1-pound test raised the tissue samples to 41 parts per million.

Espinoza cautions that this is just one year of data, and no one should act on this alone.

Paraphrasing Descartes and pointing out the frustrations of working with boron, Espinoza says, “The more you study this problem, the more you realize how little you know. By studying this problem, we keep raising questions. Why does the deficiency show up in some years and not others? Is this a physical or chemical problem? Is this deficiency going to move south of I-40? Is there a relationship between the problem and cultivars or maturity groups?”

I-40 might play the role of a “boron border” because more cotton has been grown south of the interstate. That means more concern with boron.

“According to a survey coordinated by Dr. Mozaffari, the water samples showed higher levels of boron south of I-40. We don't know if those levels are significant or not — 14 grams in 325,000 gallons. With such low numbers, it could even be lab error. However, tissue samples south of I-40 also show higher levels of boron.

“It's very strange. You may see both sufficiency and deficiency at the same soil test levels. Hopefully, in the end, we will be able to have a predictive tool allowing us to know where, when and under which conditions we can expect deficiencies. The only way to get to that point is to better understand how to deal with this nutrient.

“We need to build a database and raise awareness. Dr. Mozaffari will continue conducting a survey on boron for the next several years in hopes of providing recommendations in the end.”

Farmers in areas where this problem has been identified should consider applying 1 pound of boron per acre with their normal fertilizer applications, says Espinoza.